It is known that the driving of an aircraft on the ground, that is to say the yaw control of said aircraft, is chiefly effected by the rudder and the steerable nose gear, disposed near the nose of the latter (commonly called the “nosewheel”). For this purpose, the rudder and the steerable nose gear are controlled from a rudder bar, at the disposal of the pilot. A depression to the right, for example, of the rudder bar conveys the desire of the pilot to produce a yawing moment tending to move the nose of the aircraft toward the right, this yawing moment being obtained by a rightward deflection of the rudder and of the steerable nose gear.
It is known moreover that ground braking of aircraft is ensured by brakes installed on the wheels of the undercarriage legs, as well as by spoiler flaps (airbrakes) capable of increasing the drag of the aircraft and of holding it hard down on the ground so as to increase the effectiveness of the brakes of the wheels and/or by thrust reversers, the wheel brakes being controlled by a system capable of taking into account commands coming from the pilot or from an automatic device. To brake the aircraft on the ground, the pilot has two pedals mounted on the rudder bar and associated respectively with the brakes of the wheels disposed on either side of the longitudinal axis of the aircraft: thus, the right pedal can control the brakes disposed on the right of the aircraft and the left pedal can control the brakes disposed on the left. If he exerts different braking actions on the two brake pedals, the pilot produces differential braking between the wheel sets disposed on either side of the longitudinal axis of the aircraft, this differential braking producing a yawing moment for the aircraft.
The driving of an aircraft on the ground can therefore also be obtained by such differential braking. Thus, when the pilot of the aircraft wishes to correct the lateral path of the aircraft on the ground, he can act on the rudder bar, to involve the rudder and the steerable nose gear, and/or on the brake pedals, to produce differential braking.
It should however be noted that action on the brake pedals alone may, under certain conditions such as strong sidewind, engine failures, etc., be insufficient to control the lateral path of the aircraft and lead the latter to go off the taxiway.
Now, such a situation can occur in the event of failure of the rudder bar. Specifically, in this case, only the brake pedals are available for yaw control of the aircraft during its ground run.